A new approach to explain the ?high irradiance responses? of photomorphogenesis on the basis of phytochrome

Abstract

A new approach to explain the “high irradiance responses” of photomorphogenesis on the basis of phytochrome is described. Irradiance and wave-length dependency of different phytochrome reaction models are analyzed. 1) An open phytochrome model which is based on spectophotometric data (Schafer, 1972; Schafer et al., 1972; Schafer and Mohr, 1974) and describes only the induction phenomena is presented; 2) A closed phytochrome-receptor model which is based on the analysis of phytochrome-receptor interactions (Quail et al., 1973a. Quail and Schafer, 1974) describes the principal behavior of high irradiance responses, namely, optimum quantum responsivity in the far-red and blue part of the visible spectrum and the irradiance dependency. This model cannot account for the induction phenomena; 3) An open phytochrome-receptor model which describes both the properties of the induction responses, as well as those of the high irradiance responses, is tested for its physiological relevance by comparing the predictions based on this model with the measured data for phytochrome controlled anthocyanin synthesis (Wagner and Mohr, 1966) and suppression of lipoxygenase synthesis in the mustard seedling (Oelze and Mohr, 1973).